PCB raw laminate materials:
FR2 (abreviation for Flame Resistant 2) is probably the oldest material used for PCB production, it’s a paper impregnated with a phenol formaldehyde resin.
Still used for low cost consumer electronics single side PCBs, easy to punch, stamp, drill. Very cheap, tends to absorb humidity so not very good for anything else.
Not suitable for plated through hole process as the temperature expansion coefficient of paper and copper is quite different and cause plating cracking at high / low temperatures.
Still there are lot of TVs, VCRs, white appliances which have PCBs inside with FR2 material.
CEM (composite epoxy material) there are two types of CEM laminates CEM-1 is made of cellulose paper core between two layers of continuous woven glass fabric, impregnated with a flame resistant epoxy resin binder. CEM-3 laminates are similar, but with a chopped glass fiber core instead of paper. CEM have better characterictics than FR2 but still not good for plating due to same reason – plating cracking caused by the big temperature expansion differences.
FR4 (Flame resistant 4) material is woven fiberglass cloth with an epoxy resin filler. This is the most widely used PCB material for double sided and multilayer PCBs at the moment.